Real-Time MRI-Guided 3-Fraction Accelerated Partial Breast Irradiation in Early Breast Cancer

This trial will investigate a novel 3-fraction radiation regimen for participants undergoing breast-conserving therapy (BCT) for early breast cancer that will: 1) significantly reduce the duration of treatment and can be completed in one-week (5 working days) and 2) MRI-guided radiotherapy (MRIdian) would limit the volume of normal tissue radiated and therefore resultant toxicity. The hypothesis is that 3-fraction radiation therapy can be delivered safely without compromising the therapeutic ratio. Participants can expect to be on study for follow up up to 5 years.